Host response to infection of a subperiosteal hydroxylapatite implant

Particulate, nonresorbable hydroxylapatite is currently a popular implant material for the augmentation of atrophic alveolar ridges. Most reports have demonstrated favorable biocompatibility with common usage, but how the host bone will respond to the implant in the presence of an infection has not yet been investigated. Hydroxylapatite was implanted subperiosteally on one side of the mandible in four New Zealand White rabbits. After 3 months were allowed to elapse for stabilization of the implant, an infection was induced in both sides of each mandible by inoculation with Bacteroides melaninogenicus. One month later the animals were put to death and both sides of each mandible were examined microscopically. On the nonaugmented side there was total resolution of the infection. The side of each mandible containing the hydroxylapatite implant showed very mild chronic inflammation throughout the medullary space and periosteum. Although the number of animals used was small, the results suggest that the presence of the hydroxylapatite implant may have interfered with the host's ability to resolve the infection in the underlying bone. The possible mechanism of this interference is discussed.